Silly, foolish or stupid or ridiculous, the opposite of serious.

He's being silly, so we should just ignore him.

That's a silly idea, so I don't think she means what she's saying.

Amazing, to be incredible or so good as to be hard to believe, the opposite of ordinary.

That company's new products are truly amazing.

She gave an amazing performance, especially after all the difficulties she had overcome.

Crucial, to be of extreme importance or an essential part, the opposite of optional.

It's crucial that we get them to sign the contract by the end of the week.

Getting that data is crucial for our success.

Impressive, to stand out and be unforgettable in a good way.

His presentation was so impressive that we decided to hire him right away.

They have an impressive website, but the quality of their products is pathetic.

Realistic, to be possible and attainable.

That deadline isn't realistic, so we need to ask for more time.

He isn't being realistic when he expects to charge such high prices for his products.